1. Field of the Invention
The present invention relates to a speed-change-gear-type automatic transmission system for vehicles.
2. Description of the Prior Art
Recently, there are being put into practical use an increasing number of automatic transmission systems of the speed-change-gear type which, having actuators responsive to electric signals provided in association with the transmission and clutch, are capable of automatically carrying out start and gear change operations in accordance with parameters indicative of the operating condition of the vehicle, such as the amount of depression of the accelerator pedal.
Up to now the minimum speed at which a vehicle having an automatic transmission system of the type described above could be driven has been determined in all cases, other than when the clutch is disengaged or when the vehicle is being accelerated from rest, by the minimum engine speed and the speed reduction ratio of the lowest gear (e.g. first gear or reverse gear). Therefore, the minimum driving speed in first or reverse gear has normally been 3 to 5 km/h. Practically, however, it often becomes necessary to drive a vehicle at a slower speed than this minimum driving speed, as in the case where the vehicle is to be driven into a garage. In such a case, the driver usually depresses the brake pedal to cause the clutch to disengage, thus realizing the desired very low driving speed. This difficulty encountered by the driver in driving the vehicle at very low speeds has constituted a major disadvantage of speed-change-gear-type automatic transmission systems of the prior art.